The station master of the central Greek city of Larissa was arrested on Wednesday, police said, hours after a head-on collision between two trains left at least 46 dead, according to local media reports.

A passenger train with 346 people aboard collided with a cargo train in Greece on Tuesday night, resulting in heavy casualties – the country's deadliest rail crash in decades.

The crash occurred as the passenger train emerged from a tunnel. Derailed carriages, badly damaged with broken windows and thick plumes of smoke, could be seen on the site, where rescuers were looking for more survivors.

Greece on Wednesday declared a three-day national mourning from March 1 to 3 for the victims of the train accident, local media reported. During the mourning, the Greek flag will fly at half-mast at all public buildings, and all public celebrations are canceled. 

Greek President Katerina Sakellaropoulou cut short her visit to Moldova and returned to Greece on Wednesday. She visited the site of the train accident and two Larissa hospitals where the crash victims were taken.

It remains unclear what caused the train crash so far.

Greek Prime Minister Kyriakos Mitsotakis on Wednesday promised to find out what caused the tragedy and "do everything in our power to make sure it never happens again" as he expressed his condolences on social media, saying, "We are experiencing today as a country."

So far, no Chinese casualties have been reported in the train collision, the Chinese Embassy in Greece told China Media Group.

(With input from Reuters)